Paving compositions and methods of making the same



United States Patent N 3,091,543- Patented lifiay 28, 1963 3,091,543 PAVING COMPOSITIONS AND METHODS 0F MAKING THE SAME Edmund 0. Rhodes, Pittsburgh, Pa., assignor to Curtiss- Wright Corporation, a corporation of Delaware Filed July 23, 1959, Ser. No. 829,041 4 Claims. (Cl. 106-279) This invention relates to improved paving structures, and more particularly to bituminous compositions for use in their construction.

As is commonly known, asphalt cements are widely used as binders in the construction of highway surfaces, airport surfaces, and other types of pavement, whether these surfaces are produced by the plant-mix or penetration-macadam procedures. Also used for such purposes, but to a lesser extent, are the standard grades of coal tar designated as RT-ll and RT-lZ -by the American Society for Testing Materials and the American Association of State Highway Oiicials.

Each of the two types Of binder, namely asphalt cements and road tars, has certain advantages and disadvantages not possessed by the other that are attributable mainly to inherent differences in the raw materials from which they are produced, that is, asphalt from petroleum and road tars from coal tar.

Asphalt cements are better adapted to the present operating conditions at most hot-mix plants, where the mixing temperatures of aggregates and cements range between 275 F. and 325 F. and the temperatures of the mixes at time of laying are usually within a range of 225 F. to 325 F.

On the other hand, owing to the vaporization of volatile components of such coal tar cements as RT-ll and RT-lZ at higher temperatures, the preferred temperature range for them is approximately 175 F. to 250 F. and the temperatures of aggregates and fillers to which they are added should not exceed 225 F. Because of these lower required aggregate and binder temperatures, the substitution of coal tar cements for asphalts in hotmix plants results in lower drying and mixing capacities.

An advantage under service conditions of asphalt cements over coal tar cements of the prior art is a superior viscosity-temperature relationship, more -commonly referred to as temperature-susceptibility. The greater change in consistency with change in temperature that takes place in a typical coal tar cement as contrasted with a typical asphalt cement is illustrated by the data in Table I. In-this table are compared the consistencies of the two cements of the prior art, as measured by the Standard Method of Test for Penetration of Bituminous Materials, ASTM test D5-52. In accor-dance with this test a standard needle bearing a load of 50 grams was placed with the point in contact with the material and allowed to penetrate for 5 seconds, with the material first at 25 C. and then at 32cl C., and the depth of penetration in hundredths of a centimeter was observed.

It will be observed that the increase in penetration with rise in temperature was much greater for the coal tar cement than for the asphalt cement. To offset the lower softening points of tar cements and their greater tendency to soften under service conditions with rise in temperature, it has been customary to use more densely graded aggregates in the construction of tar concrete and penetration-macadam tar pavements, in order to obtain stabilities comparable with those of asphaltic concretes and asphalt penetration-macadams having somewhat more open aggregate gradings. This necessitates the use of more filler, and more accurate proportioning of the aggregate, filler, and binder when using coal tar cements.

Contrasted with the above disadvantages resulting from the use of coal tar cements in paving structures, however, laboratory and service comparisons have proved that properly constructed paving structures employing tar cements are superior in several important respects to paving structures employing asphalt cements.

Tar cements adhere more strongly to most aggregates, and deteriorate less on contact with or immersion in water for prolonged periods of time; they are much less soluble in jet fuels, gasoline, lubricating oils, fuel oils, and other petroleum distillates and residuals; they impart greater and more permanent skid resistance to pavements in which they are incorporated, and show a greater tendency to self-heal if cracking of such pavements occurs.

It is therefore a primary object of this invention to provide a binder material for paving which has the desirable attributes of both the asphalt and coal tar cements of the prior art.

It is another object of the present invention to provide a binder suitable for use under the currently practiced mixing conditions and at the usual operating temperatures.

It is also a principal object of this invention to provide improved binders that will have temperature-susceptibilities superior to those of coal tar cements and comparable to those of asphalt cements.

A further object is the provision of a binder material suitable for the gradations of aggregate generally used in hot-mixes and penetration-macadams.

Another object is to provide a binder capable of maintaining continued strong adhesion to aggregates.

Still a further object of the invention is the provision of a binder composition less subject to deterioration on prolonged contact with or immersion in water.

Yet another object is to provide a bin-der having minimum solubility in petroleum distillates and residuals.

A further object of the present invention is the provision of a highly skid-resistant paving structure.

Still another object is to provide a paving having selfhealing quality.

The foregoing objects and advantages of the invention, and others ancillary thereto, will be readily understood on reading the following specification in connection with the accompanying drawing, in which is shown a fragmentary cross-section in elevation of a paving structure fabricated according to the invention.

In making a binder possessing the advantages enumerated above, bituminous coal is dissolved or colloidally dispersed in coal tar, or in a mixture of coal tar and coal tar oil, in accordance with a process similar to that disclosed in U.S. Patent No. 1,925,005, issued August 29, 1933, to Harold l. Rose and William H. Hill, on a process for making a homogeneous product lower in ash and sulfur content than raw coal.

However, in the present invention the process is carried out in such a manner as to produce binders particularly adapted for use in the construction of highway and airport surfaces of the bituminous concrete type, and sur-.

of the coal, to remove volatile constituents which would evaporate excessively during the hot-mixing operation or from the linished pavement. The precise state of the coal in the digestion product, whether a true solution or a colloidal dispersion, is not known, and it will be understood that the two terms as used herein are intended to be synonymous.

The following examples illustrate some of the ways in which the invention has been carried out.

Exam-ple I Distilled coke-oven coal tar, having a softening point of 33 C. and conforming with all the requirements of ASTM Specification D490-47 for grade RT-12, in the proportion of 89.2% by weight was mixed at room temperature with 10.8% of finely ground bituminous coal having the following proximate analysis: moisture 0.48%, volatile material 23.14%, fixed carbon 61.41%, ash 14.97%; the sulfur content was 5.16%.

This mixture was heated in an autoclave with the vent open (no pressure) and with agitation, to remove water and low-boiling distillates. When the temperature reached 400 F. the vent was closed, and heating was continued until the temperature of the mixture reached 600 F. The temperature was then maintained between 600 F. and 620 F. for one hour, during which time the pressure in the autoclave was approximately 20 p.s.i. Heating was then discontinued, the autoclave was cooled until the temperature of the charge had dropped to 400 F., the vent was opened, and the finished binder was drained into a receiver.

Example Il The coal used in Example l, in the proportion of 11.4% by weight, was mixed at room temperature with 64.4% of coke-oven coal tar pitch having a softening point of 45 C. and 24.2% of high-boiling coal tar oil having a distillation residue at 355 C. of approximately 75%.

This mixture was charged into the autoclave, heated to 600 F. and held at approximately that temperature for one hour with the vent of the autoclave open (no pressure). After cooling to 400 F. the finished binder was withdrawn from the autoclave.

Example III Crude low-temperature tar made from bituminous coal was heated to 598 F. in the autoclave with the vent open to remove 25.9% of distillate. The residual pitch, with a softening point of approximately 32 C., was mixed at room temperature in the proportion of 64.4% with 24.2% of high-boiling coal tar oil like that used in Example II, and 11.4% of coal like that used in Examples I and II.

This mixture was heated in the autoclave to 400 F. with the vent open, and then to 600 F. with the vent closed. The temperature was maintained at 600 F. for an additional hour with the vent closed; the maximum pressure developed during this period was approximately 40 p.s.i. The mixture was then cooled to 400 F., the vent opened, and the finished binder discharged.

Example IV Crude low-temperature tar was mixed at room temperature with bituminous coal in the proportion of 96% tar to 4% coal. The coal used in this case was not finely ground as in the preceding examples, but had a particle size ranging from 3/8 down to No. 10 screen size. Its approximate analysis was as follows: moisture 0.81%, volatile matter 23.61%, iixed carbon 68.09%, ash 7.49%; its sulfur content was 1.27%.

This mixture was heated to 569 F. in the autoclave with the vent open to a condenser which recovered distillate amounting to 20.2% of total weight. The vent was then closed and heating was continued, maintaining the temperature of the charge at approximately 600 F. for one hour. After cooling to 400 F. the finished binder,

amounting to 73.6% by weight of the Original charge, was drained from the autoclave.

In order to compare the four coal digestion binders of the present invention, made as described above, with a typical asphaltic, hot-mix binder and with a representative tar binder of the prior art, each of the six binders are subjected to the following tests.

SOFTENING POINT, RING-AND-BALL METHOD, ASTM D36-26 A brass ring of 5/3 internal diameter and 1A depth is filled with the molten material to be tested. After cooling in water at 5 C. (41 F.) for 15 minutes, a 34s" steel ball is placed in the center of the upper surface of the sample. The ring containing the sample isthen suspended 1" above the bottom of a beaker containing freshly boiled distilled water at 5 C. and 2" below the surface of the water. Heat is applied in such a manner as to raise the temperature of the water by 5 C. each minute. The temperature of the water at the instant when the bituminous material touches the bottom of the vessel is reported as the softening point.

SPECIFIC GRAVITY AT 25 C., ASTM METHOD D71-52 By means of a specific gravity balance a 1/2 cube specimen of the binder was weighed in water and in air at 25 C. The specific gravity of the binder was then calculated as follows:

Wt. of sample in air Wt. in air-wt. in Water PENETRATION AT 25 C. AND 32 C., ASTM METHOD The depth in hundredths of a centimeter to which a Specific gra vity= standard needle 2" long and 1.0 to 1.02 mm. in diameter puted as follows:

Penetration increase per C.

* Pen. 32 C.-Pen. 25 C. 7

STRIPPING OF BINDER FROM AGGREGATE-IN WATER In this test 50 grams of amixture containing 98% by weight of 20-30 mesh Ottawa sand and 2% of the binder to be tested was agitated vigorously for 15 minutes in water heated to 140 F. The mixture of water and sample was then transferred to a Ztl-mesh sieve and uncoated (stripped) sand particles were washed through the sieve and into a pan by means of a stream of water heated to approximately 140 F. After decantation of the water from the uncoated particles the latter were dried in the pan and weighed. By multiplying the weight by 2 (since the original weight of the sample was 50 grams), the percentage of stripped particle-s was determined.

SOLUBILITY IN JET FUEL (J P-4) .Tet fuel (IP-4) in the amount of 100 ml. was added to grams of a mixture containing 98% of 20-30 mesh Ottawa sand and 2% of the binder to be tested. The ask containing the above materials were placed in an automatic shaker and agitated vigorously for 15 minutes. The JP-4 was then decanted from the sand-binder mixture and the latter was washed with two 50 ml. portions of fresh .TP-4. One-fifth (40 ml.) of the total .IP-4 solution was then withdrawn by means of a pipette and transferred to shallow dishes for partial evaporation on a water bath. Evaporation was then continued in an oven to substantially constant Weight. The latter multiplied by 5 and divided by 2 (grams of binder in the mixture) gave the fuel.

MARSHALL STABILITY AND FLOW DETERMINATION A graded limestone aggregate with approximately 7% percent of binder dissolved by the jet passing through a #200 sieve and 100% passing through a 3/s" sieve was mixed at about 300 F. with the optimum proportion of binder as determined by previous tests. Briquets of 4" diameter and approximately 2%" high Specific gravities of binders made in `accordance with this invention are appreciably higher than those of asphalt cements and somewhat higher than those of tar cements made in the usual manner. Binders of low specific graviwere made in a mold from the mixture, using 50 blows 5 ties iwhich, in .the case of asph-alt cements approach the of the standard Marshall compaction hammer on each specific gravity of water, have a greater tendency to oat end of the specimen. The briquets were allowed to cure or bleed to the surfaces of pavements in which they are in air for at least 24 hours. They were then immersed employed and lead to the formation of surfaces that are for 25 minutes in a water bath at 140 F. and tested imdangerously slippery when wet. mediately with a Marshall test assembly in an Instron The superior temperature susceptibilities of binders testing machine. Maximum load (stability) and deformade in accordance with the present invention is shown mation (flow) at the time of failure were recorded. by their penetration increases per degree rise in temperature between C. and 32 C. They are all much lower CHANGE IN STABIIsAEgATER IMMERSION than that of the typical coal tar binder and approximately 15 the same as that of the typical asphalt cement. The Graded llmsoue aggfegaie Passing 34s" slsVe aud feability of the present invention to produce pavement bindalled 0n a #l0-s1eve Was mlXed W1lh 4% 0f each bmdefers that will soften less lat elevated temperatures and Bflquels 0f 4" dlameel and 21/2" height were then mail@ become less hard and brittle at lower temperatures is from the mixture using Marshall test equipment. Temshown .by these comparisons Peratues 0f ugggega and binder at the time 0f {nixiug 20 The binders of the present invention do not show the Were about 300 F- and the number 0f blows Wllll the high tendency of asphalt binders to separate from aggrestaudard lampes Was .50 011 each und 0f each briquet gates on prolonged contact iwith or immersion in water. After atmospheric cooling for at least 8 hours the briquets Stripping of the Sort which Tesults from such separation were lmmefsed lm Water at 120 F- for four days- They results in .the early destruction of pavements and is highly were then placed in water at 140 F. for 25 minutes and 25 undesimbla tested immediatelyin the Marshallassembly with Instron v AS indicated by Mal-Shall stabilities, the load bearing -eqmpmem to Pfovlde the Compressloncapacities of pavements made with binders produced in FLOW TEST AT ATMOSPHERIC TEMPERATURE accordance with the present invention are much higher nt 'i1 h l en Usingra mold of the type prescribed by ASTM Method 21221111 gronrrsmgts gr in g asp at cem ts or D61-38 (Softening Point of Tar Products, Cube-in-Water S es. tane topdefomon e ultim f om ab Method), 1/2" cubes were prepared from each of the six upenor .r 1S e 1 r s g r binders. The six cubes were then placed at the top of a Formally hlgh Wheel loadings and Channehzed trame 1S stainless steel plate inclined 30 from -the horizontal. ufdlcafed by the 10W, Marshall ow Values o? the coal The temperature of the room in which the test assembly dlgsmon bmders typlfymg the pm sent lflventlon was placed varied from 26 C. to 28 C (78 8 F. to Binders made by the present invention have much 82.4 F,) The Way in which each Cube deformed and lower solubilities than yasphalt cements in petroleum disiiowed downwardly on the inclined plate was observed till-aies 0I' residuals -iIl general and iet fuels, such 'as TP-4, and measured after 4 hours, 161/2 hours, and 221/2 hours. iu Particul'al- The importance 0f this difference especially Analytical data resulting from the application of the on airport surfaces .Where jet fuel spillage leads to the tests described above to each of the six binders are preearly destruction of asphalt pavements is readily apparent. sented in Table II. Further confirmation of the greater destructive effect TABLE Il l i Bindersv Made By coni 'Diges- Asphalt Coaltion Processes Binder Tar Binder 'I II III IV s0ftening1 bini, C, R a 13 51. 33.0l 50s 45.5 49.0 48.5 sp. Gravity at 25 C 1.030 1.200 1.255 1. 242 1. 225 1.183 Pen. Increase per C. (25-32 C.), 1/100 cm 6.1 26. 0 4. 7 6.8 7. 1 6. 1 Percent Stripping in water at 140 F 63. 8 0.4 24. 8 3. 4 4. 0 26.0 Marshall Stability at opt. (lbs.) 2326 1744 3350 3344 3490 3612 Mnrshaii Flow at opi. (1/1000 17. 4 7. 7 1i s. 5 s. 0 JP-4So1ubi1ity (percent ofbinder) 97.1 11.6 16.0 10.0 17.0 22.3 Change in Stability alter Water Immer n, 96

120 F., percent -17 +143 +9.() +88 0 -2 Flow dovvn 30 Incline, 26-28" Inches After 4 hours 1.06 2.19 0.94 1. 18 1.12 0.88 Flow down 30 Incline, 26-28 Inches After 16% hours l. 25 3. 13 0. 94 1. 31 1. 25 0. 94 Flow down 30 Incline, 26-28 Inches After 22% hours 1. 31 3. 38 0. 94 1. 37 1. 31 1.00

The data compared are from a typical asphalt binder of water on asphalt pavements as compared with paveaud afyplful Cual tal' binder 0f illu PUOI aft, and from 60 ments made with coal digestion binders is furnished by C0211 digestion binders made "lCCOfdlug t0 Examples l, lIl, the data for changes in stiabilities of briquets immersed HI `and 1V as dlscussed heremabovey in Water for 96 hours at 120 F. Briquets containing the It Wlll be Qbserved that all the lmdefs typlfyl'ng the typical asphalt cement showed an appreciable decrease Present ulvemlfon hal/e lsofteullg Pom/[S m 'the nlelllibr' in stability whereas some of the briquets made with binders hrodtlft afto ta typllca' B181; atcemetg mucd lgbr 65 typifying the present invention increased materially in t an at 9 a Ypma coa ar cemen e un ema y this respect yand others showed little or no change. low softening points of the usual coal tar cements cause D h 1 pavements constructed with them to `shove and rut exue to t elf ,OY/ ef softening points and greater tem' cessively unless special precautions are taken in the selec- Peratufe suscpltlbllllles, Coal -iar cements o f the present tion of aggregate gradations land use of increased ller mvelmon exhlbft much greater HOW teldencles than WPI' contents. Pavements constructed with binders of the Cal asphalt Paving Ceiueuis- Self-healing resulting from present invention wvill be less critical with respect to filler Such COldOW 1S desirable but 100 much coldflow can content and will -be more resistant to rutting or shoving result in low stabil-ities and excessive deformation under than pavements made with asphalt cements or ordinary high rwheel loadings. By means of the coal digestion coal tar binders. process, that is the subject of this invention, it is possible to control coldow so as to approximate or duplicate that of asphalt cements if desired.

vIt is therefore apparent from. a consideration of the data in Table II that the binders. made by the present invention preserve the `desirable characteristics of both the asphalt and the tar of the prior art, in some4 cases even improving on both.

Referring now to they drawing, there is shown a fragmentary elevation in cross-section of. a. paving structure incorporating. the binder. material. of the invention. The subgrade- V11 is excavated to a depth suitable for the class of road to be built. On the subgrade is laida base course 12 comprising coarse aggregate-and suitable filler material, disposed in the interstices thereof. A binder course 13, comprising aggregate of particle size from about one inch. down to five percent passing a 200-mesh sieve, hot-mixed with about 4% to 7% of any of the binders made in accordance with the present invention, is laid on the base course and compacted. by rolling. Lastly, there is laid asurface or Weavingtcourse 14, comprising aggregate having a particle size from one-half inch down todust, hot-mixed with about 4% to 8% of one of Vthe present binders, and compacted by rolling to` a firm, tightly sealed surface. The edges of the road are finished off by a berm 15.

It will be understood that various changes and modifications may be made Without ydeparting from the scope of Ithe invention, and it is intended to cover such modi cations in the appended claims.

What is claimed is:

l. A method of making paving cement,. comprising in combination lthe steps of mixing at room temperature approxi-mately 90% of distilled coke-oven tar having a softening point of 33' C. with approximately 10% of finely Iground bituminous coal, heating said mixture in an autoclave without pressure to approximately 400 F. to remove water and low-boiling distillates, then heating said mixture under approximately p.s.i. pressure to approximately 600 F., maintaining said mixture under said pressure at a temperature between 600 F. and 620 F. for approximately one -hour to fully digest said coal in said tar.

and to form a homogeneous composition thereof, cooling said composition to approximately 400 F., releasing said pressure, and recovering the digestion product.

2. A method of making paving cement, comprising in combination the steps of mixing at room temperature approximately 65% of coke-oven coal tarY pitch having a softening point of 45 C. with approximately 1\1% of finely ground bituminous coa-l and approximately 24% of high-boiling coal tar -oi-l having `a distillation residue at 355 C. `of approximately 75%, heating said mixture to about 600 F. and. maintaining `said mixture at' approximately 600 F. for approximately. one hour to fully digest said coal' in said pitch and said oil and to form a homogeneous composition thereof.

3. A method of making paving cement comprising in combination t-he steps of heating low-temperature tar from bituminous coal to approximately 600 F. to remove distillate .in the -amount of about 26% `of the starting yweight and to leave a residual pitch with a softening point of :approximately 32 C., cooling said pitch, mixing said pitch at room temperature in the proportion of approximately with approximately 24% lof yhigh-boiling coal tar` oil and approximately V11% of iinely ground bit-uminous coal, heating said mixture in an autoclave without press-ure to approximately 400 F. to distill off volatile components, then heating said mixture to -approximately 600 F. under approximately 40 p.s.i. pressure maintaining -said mixture `at about 600 F. under said pressure for approximately one hour to ful-1y digest said coal. in said pitch and said; oil and to Aform a homogeneous. composition thereof, cooling said composition to approximately 400 F., releasing said pressure, and recovering the digestion product.

4. A methodv of making paving cement, comprising in combination the steps of mixing approximately 96% of low-temperature coal tar at room temperature with approximately 4% of crushed bituminous coal having particle sizes ranging from No. 10 screen size to heating said mixture in an autoclave to a temperature in the neighborhood of 600 F. Without pressure to distill off volatile components in the amount of approxi-mately 20% by weight of the original mixture, and maintaining the residual mixture at approximately 600 F. under approximately 20 p.s.i. pressure for about one hour to fully digest said coal in said tar and yto form a homogeneous composition thereof.

References Cited in the tile of this patent UNITED STATES PATENTS Re. 9,207 Bailey May 18, 1880 875,196 Lovejoy Dec. 31, 1907 1,500,451 Hacker July 8, 1924 2,629,669 Anderton Feb. 24, 1953 2,861,895 Hardman Nov. 25, 1958 2,888,357 Pittman et al May 26, 1959 FOREIGN PATENTS 334,336 Great Britain Sept. 4, 1930 

1. A METHOD OF MAKING PAVING CEMENT, COMPRISING IN COMBINATION THE STEPS OF MIXING AT ROOM TEMPERATURE APPROXIMATELY 90% OF DISTILLED COKE-OVEN TAR HAVING A SOFTENING POINT OF 33*C. WITH APPROXIMATELY 10% OF FINELY GROUND BITUMINOUS COAL. HEATING SAID MIXTURE IN AN AUTOCLAVE WITHOUT PRESSURE TO APPROXIMATELY 400*F. TO REMOVE WATER AND LOW-BOILING DISTILLATES, THEN HEATING SAID MIXTURE UNDER APPROXIMATELY 400* F., RELEASING SAID MATELY 600*F., MAINTAINING SAID MIXTURE UNDER SAID PRESSURE AT A TEMPERATURE BETWEEN 600*F. AND 620*F. FOR APPROXIMATELY ONE HOUR TO FULLY DIGESST SAID COAL IN SAID TAR AND TO FORM A HOMOGENEOUS COMPOSITION THEREOF, COOLING SAID COMPOSITION TO APPROXIMATELY 400*F., RELEASING SAID PRESSURE, AND RECOVERING THE DIGESION PRODUCT. 